Rainer K. Sachs

Rainer Kurt "Ray" Sachs (June 13, 1932 – April 16, 2024) was a German-American mathematical physicist, with interests in general relativistic cosmology and astrophysics, as well as a computational radiation biologist.

In 1937 the family left Germany to flee from Nazi persecution, and settled in the United States, so Rainer Sachs is generally considered an American scientist.

He received his bachelor's degree in mathematics from MIT in 1953 and his PhD in theoretical physics from Syracuse University in 1959.

In 1967, he and Arthur M. Wolfe were the authors of the Sachs–Wolfe effect, which concerns a property of the Cosmic microwave background radiation.

[4] The Ehlers–Geren–Sachs theorem, published in 1968 by Jürgen Ehlers, P. Geren and R. Sachs, shows that if, in a given universe, there exists a reference frame at each event such that the cosmic background radiation is isotropic, then under certain conditions that universe is an isotropic and homogeneous FLRW spacetime.